Does aerobic exercise increase hippocampal volume?

What the latest evidence shows: no reliable increase in hippocampal volume for healthy older adults

The most rigorous evidence to date—meta-analyses pooling multiple randomized controlled trials—shows that aerobic exercise does not significantly increase hippocampal volume in cognitively normal older adults. A 2023 meta-analysis of eight trials with 554 participants found no significant effect (standardized mean difference = 0.10, p = 0.073), even though exercise did improve cardiorespiratory fitness [2]. A separate 2025 meta-analysis of 12 studies with 774 participants came to the same conclusion: no statistically significant effect on hippocampal volume (SMD = 0.09, p = 0.20) [9]. These results mean that for a healthy person over 50, starting an aerobic exercise program is unlikely to enlarge the hippocampus.

Even a well-designed one-year trial found that aerobic exercise did not prevent age-related brain volume loss. In fact, the stretching control group showed less hippocampal shrinkage than the aerobic group (p = 0.040 for interaction) [1]. This surprising finding underscores that the relationship between exercise and hippocampal volume is not straightforward. The same study did find that improvements in cardiorespiratory fitness correlated with better cognitive performance and thicker cortex in some brain regions, suggesting exercise benefits cognition through other mechanisms [1].

When exercise might help the hippocampus: specific populations and mechanisms

While the evidence is negative for healthy older adults, aerobic exercise does show promise for certain groups. In patients with type 2 diabetes, one year of moderate aerobic training significantly increased total and right hippocampal volume compared to a control group (p = 0.027 and p = 0.043, respectively), and also improved scores on cognitive tests [5]. Similarly, a pilot study in people with multiple sclerosis found that three months of stationary cycling led to a 16.5% increase in hippocampal volume and a 53.7% improvement in memory, with no comparable changes in the stretching group [10]. These findings suggest that exercise may be most beneficial when the hippocampus is already compromised by disease.

Exercise may also protect the hippocampus by improving its blood supply, especially in people at genetic risk for Alzheimer's disease. In a one-year trial, hypertensive carriers of the APOE4 gene (the strongest genetic risk factor for late-onset Alzheimer's) who exercised showed a significant increase in hippocampal blood flow (4.09 mL/100g/min) compared to a decline in the control group (-2.08 mL/100g/min) [11]. This improvement was linked to reductions in systolic blood pressure, suggesting that exercise benefits the hippocampus through vascular health in high-risk individuals [11]. Additionally, in people with Alzheimer's dementia, aerobic exercise slowed the progression of white matter hyperintensities (a marker of small vessel disease) by more than 50% compared to stretching, though it did not prevent hippocampal shrinkage [4][6].

Why the older claims fell apart: methodological issues and the role of fitness

Earlier, smaller studies and animal research suggested that aerobic exercise robustly increases hippocampal volume, but these findings have not held up in larger, better-controlled human trials. The 2023 meta-analysis noted that methodological limitations across studies—such as small sample sizes, lack of harmonized MRI measurement techniques, and insufficient statistical power—may have masked true effects or produced false positives [2][3]. For example, one early pilot study in multiple sclerosis reported a dramatic 16.5% increase in hippocampal volume after just three months of cycling, but this was based on only two participants [10]. Such results are intriguing but not generalizable.

Another key point is that improving cardiorespiratory fitness does not automatically translate to hippocampal growth. The 2023 meta-analysis found that while exercise moderately improved fitness (SMD = 0.30, p = 0.005), this improvement was not associated with changes in hippocampal volume (p = 0.923) [2]. Similarly, a one-year trial in older adults with elevated brain amyloid found that exercise improved fitness by 11% but had no effect on brain volume or cognitive performance [7]. This suggests that the cognitive and brain benefits of exercise reported in some studies are likely due to mechanisms other than increasing hippocampal volume—such as improved blood flow, reduced inflammation, or enhanced synaptic plasticity [7][8].

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